The present invention relates to a security document, particularly of the type comprising a flat support; one or more identification codes, either optical, magnetic or of any other type; and a hologram.
Security documents (such as passports, credit cards, security passes, etc.) are known to be affixed with holograms, the sole function of which is to enhance the appearance of the document; the authenticity of the hologram generally being checked only macroscopically by means of visual inspection by authorized personnel.
Other known types of security documents present holograms for the other purpose of preventing forgery, and which may be embossed either internally (embossed type) or externally (transfer foil type). Holograms of this sort, however, fail to meet two requirements essential for this type of application:
Protection of the hologram against physical-chemical agents in the environment and mechanical, thermal stress, etc., which may impair the quality of the image. This is particularly essential in cases where the document is checked automatically by devices designed to perform a programmed analysis of all and part of the image.
Preventing the hologram from being removed from the original and affixed to a forged document.
This is the case, in fact, with current types of "embossed" holograms, which may easily be detached from the surface to which they are glued, and affixed to other forged documents.
"Transfer foil" types of holograms, while being preferable to the "embossed" type in that they are secured to a number of supports with a layer of heat-setting adhesive, have a very thin metalized surface layer with no protection and, therefore, very little resistance to bending and abrasion. This inevitably, results in wear and scoring of the holographic diffraction grating and, consequently, loss of data and references during both integral and partial analysis of the original holographic image.